Pedestal switch insulator



Patented Dec. ll, 1934 UNITED STATES PATENT GFFICE to Locke Insulator Corporation,

Baltimore, Md.,

a corporation of Maryland ApplicationApril 24, 1931, Serial No. 532,625

1 Claim.

The inventionY relates to insulators, particularly those of that type in whichv there is a plurality of units mounted and secured in superposed relation to form a stack which may be used for the support of a bus bar, switch or the like.

In insulators ofA this general type it has been found that one of the chiefdifculties experienced is the lack of stiffness in tall insulator stacks. In other words the ordinary variety is not well capable of withstanding any great degree of cantilever strain.

It is with the above facts in view that I have devised the present invention which has for its general object the provision of a novel construction and design of insulator formed of similar units secured together in superposed relation or series, the construction of the individual units being such as to obtain the maximum mechanical strength, rigidity and stiffness without impairing the electrical efficiency as regards flash-over value, puncture strength, etc.

Another important object of the, invention is to provide an insulatorof this character in which the individual units are of such construction that the stack may be graded, that is to say the construction is such that use is made of the internal capacitance of the units for equalizing the potential in the electro-static eld and preventing any concentration of forces such as might be conducive to a flash-over orf-other similar electrical failure.

Another object of the invention is to provide an insulator of the nested porcelain shell type, of course with suitable terminal hardware, and in which metallic elements are associated interiorly with respect to the porcelain shells or elements for the purpose of providing the proper capacitance necessary to effect grading of the stack.

An additional object is to provide an insulator of this character in which any desired number of units may be used, and in which each unit will be simple and inexpensive to make, all the units easy to assemble, and the entire structure efficient and durable in use, and also a general improvement in the art.

To the attainment of the foregoing and other objects and advantages, the invention preferably consists in the details of construction and the arrangement and combination of parts to be hereinafter more fully described and claimed, and illustrated in the accompanying drawing in which:

The figure is a view partly in elevation and partly in section through the top unit and a portion of the adjacentl unit' ofA a stack of insulators constructed in accordance with the invention'.

Referring more particularly to the drawing the numeral 10 designates broadly, and as a whole, the topmost unit of a stack which may consist of any desired number of units in superposed relation and which may be utilized for the support of a bus bar, switch or the like, the exact purposel being immaterial. This unit'is shown as comprising nested porcelain shells or sections 11 and 12, the former carryingA a metal cap 13, and the latter being mounted upon a. hollow metal pin 14 which is in turn adapted to be carried by the cap 13 of a unit immediately below. The upper shell 11, constructed preferably of porcelain, comprises a skirt 15, a petticoat 16, and an upstanding neck or headV 17 which is' of inverted frusto-conical shape or outwardly ared and which preferably has-a concavedcentral top surface 18. At its underside this section is formed with a recess or cavity 19vwhich receives the upstanding stem or neck 20 of the vsection 12. This section 12 is represented as having a corrugated exterior surface 21 for the purpose of increasing the current leakage distance and is also formed with a recess or cavity 22 Whichfreceives the cylindrical upper end portion 23 of the pin 14. The cap 13 is secured to the-neck 17 of the topmost section by cement 24, the stem or neck 20'is secured within the cavity-19 by'afmass of cement 25, and the pin portion 23 is similarly secured within the recess 22 by a mass of cement 26. It is a feature of importance to provide a metal plate or disk 27 covering the open top of the hollow pin for the purpose of serving as a dam to prevent the cement 26 from escaping through the cavity 22 into the interior of the pin. It will be noted that while the lower porcelain section l2 is shown as having an outstanding skirt 28 it may also be provided with one or more petticoats similar to the one shown at 16, if such is desired for any reason whatsoever.

Attention is directed to the fact that the lower end of the pin 14 flares outwardly and terminates in an outstanding flange 29 apertured for the passage of any desired number of cap screws 30 which enter threaded sockets or recesses 31 in the cap 13 of the unit immediately below the unit 10. The cap 13 of the unit 10 is formed with similar threaded recesses or sockets, having the same refr erence character 31 and intended to receive cap screws for mounting a clamp, switch element or l assembly or anything else desired to be supported -by the insulator stack. As the unit may be considered as a standard it is clear that any desired number of them may be arranged in stack form so as to obtain the desired height.

It is preferable that the taperedjoint beneath the cap 13 be of the lock type, that is to say it is preferable that the exterior surface of the neck or head 17 be glazed so as to avoid actual adhesion of the cement thereto, the securing action being brought about by virtue of the fact that the cement 24 acts as a lock. The interior surfaces of the cavities 19 and 22 are preierably sanded and reglazed in accordance with the method disclosed in my Patent No. 1,784,392 granted December 9th, 1930. Furthermore if such is desired a coating of asphaltum maybe applied to any of the adjacent surfaces at the cemented joints for the purpose of permitting a slight degree of relative slipping to take care of thermal strains resulting from the unequal expansionv of the metal, cement and porcelain owing to their diierent coecients of expansion.

A distinct feature of importance in my invention is the provision of means for grading the stack and I prefer to accomplish this by the internal capacitance. While it is true that all insulators are condensers to a certain limited extent, -I actually provide my insulator with interiorly located metallic elements certain of which are spaced apart by porcelain and others ci which are spaced apart by cement. Actually, I provide a metallic element` 32 within and lying against the wall of the recess or cavity 22, and also employ other metallic elements or layers 33 and 34 lying respectively against the wall of the cavity 19 and the exterior surface of the upstanding stem 20.

, In the production of Vthe insulator these metallic elements or layers may be in the nature of a metal foil suitably secured in place or may consist of a coating applied electrolytcally or as a paint, any of these different methods being considered as falling within the purview of the invention. The relative areas of these metallic layers 32, 33 and 34 will depend on circumstances such as the height of the stack or the number of units therein and the size of the unit. Furthermore at different locations in a stack it might be necessary that the extent of these layers be varied soas to bring about the proper grading of the electro-static eld about the insulator sothat any tendency toward a flash-over will be at least reduced if not entirely eliminated.

An insulator constructed in accordance with my invention is used in identically the same manner as other insulators of the stack type but it has the great advantage of possessing unusual strength and stiffness so as to be well capable of withstanding severe cantilever strains without danger of rupture oi any of the parts. Ordinarily the hardware fittings are made oi aluminum and by actual test I have discovered that my insulator possesses eight times the stiiiness of one of ordinary pattern, that is with aluminum ttings. If the hardware be of malleable iron then I have ioundV that the stiness is increased twenty-six times but of course at the sacrice of lightness. Use has demonstrated that the grading feature afforded by the interiorly located metallic layers is of great importance as tests disclose a remarkable flash-over value. It isthought from the foregoing that the construction, operation and advantages will be readily apparent to one skilled in the art without further explanation.

While I have shown and described the preferred embodiment of the invention, it should be understood that the rdisclosure is merely an exemplification of the principles involved as the right is reserved to make all such lchanges in the details of construction as will widen the field of utilityand increase the adaptability of the device provided such changes constitute no departure from the spirit of the invention or the scope of the claim hereunto appended.

Having thus described the invention, I claim:

An insulator comprising a stack of similar units adapted to be mounted in superposed contacting relation, each unit comprising a top shell of porcelain with a stem having a metal cap secured thereupon, each unit further including a lower porcelain shell having an upstanding stem cemented within a cavity in thetop shell, each unit further including a hollow metal pin with an outstanding base flange and having its upper end cemented within a cavity in said lower shell, me tallic layers within the Vfirst named cavity and upon the second named stem spaced apart with the cement therebetween andproviding capacitance means for grading the stack, and a metallic layer-.against the vinner surface of the lower shell spaced from and coacting with the metallic pin to provide capacitance.

DAVIDGE I-I. ROWLAND. 

